Mercury-manganese star

A mercury-manganese star is a type of chemically peculiar star with a prominent spectral line at 398.4 nm, due to absorption from ionized mercury.[1] These stars are of spectral type B8, B9, or A0, corresponding to surface temperatures between about 10,000 and 15,000 K, with two distinctive characteristics:

Their rotation is relatively slow, and as a consequence their atmosphere is relatively calm. It is thought, but has not been proven, that some types of atoms sink under the force of gravity, while others are lifted towards the exterior of the star by radiation pressure, making a heterogeneous atmosphere.[2]

List

The following table includes the brightest stars in this group.

Name[3] Bayer or Flamsteed designation Spectral type[3] Apparent visual magnitude[3]
Alpheratz α Andromedae B8IVmnp 2.06
Gienah Corvi γ Corvi A B8III 2.59
Maia 20 Tauri B8III 3.87
χ Lupi B9IV 3.96
Muliphein[4] γ Canis Majoris B8II 4.10
φ Herculis[5] B9mnp 4.23
π1 Bootis B9p 4.91
ι Coronae Borealis A0p 4.98
κ Cancri A B8IIImnp 5.24
14 Sagittae[5] B9p 5.89
Dabih Minor[6] β Capricorni B B9.5III/IV 6.10
HD 30963 B9 III 7.23

References

  1. ^ Mercury-manganese star. The Internet Encyclopedia of Science, David Darling. Accessed on line August 14, 2008.
  2. ^ Michaud, Georges (May 1970). "Diffusion Processes in Peculiar A Stars". Astrophysical Journal. 160: 641–658. Bibcode:1970ApJ...160..641M. doi:10.1086/150459.
  3. ^ a b c Names, spectral types and apparent magnitudes taken from SIMBAD, except as noted.
  4. ^ Muliphein Archived 2008-05-17 at the Wayback Machine, Stars, Jim Kaler. Accessed on line August 14, 2008.
  5. ^ a b Adelman, S. J. (December 1988), "Elemental Abundance Analyses with Coadded DAO Spectrograms - Part Five - the Mercury-Manganese Stars Phi-Herculis 28-HERCULIS and HR:7664", Monthly Notices of the Royal Astronomical Society, 235 (3): 763, Bibcode:1988MNRAS.235..763A, doi:10.1093/mnras/235.3.763.
  6. ^ Dabih Archived 2006-08-24 at the Wayback Machine, Stars, Jim Kaler. Accessed on line August 14, 2008.
11 Persei

11 Persei is a single star in the northern constellation of Perseus, located about 418 light years away from the Sun. It is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of 5.76.This is a chemically peculiar mercury-manganese star. Cowley (1972) found a stellar classification of B7 III(p?) (Hg?), while Hube (1970) had B8 IV, and Appenzeller (1967) showed B6 V. Stellar models indicate this is a young B-type main sequence star with an estimated age of around 51 million years. It has a low rotation rate, showing a projected rotational velocity of 4.50 km/s. The star has 3.8 times the mass of the Sun and is radiating 210 times the Sun's luminosity from its photosphere at an effective temperature of 14,550 K.

14 Sagittae

14 Sagittae is a binary star system in the equatorial constellation of Aquila. 14 Sagittae is the Flamsteed designation. It appears as a sixth magnitude star, near the lower limit of visibility to the naked eye, having an apparent visual magnitude of 5.89. The system is located 660 light years away, as determined from its annual parallax shift of 4.91 mas. It is moving closer to the Earth with a heliocentric radial velocity of –22 km/s.This is a single-lined spectroscopic binary with an orbital period of 61.5 days and an eccentricity of 0.49. The visible component is a chemically peculiar mercury-manganese star with a stellar classification of B9p HgMn. It is narrow-lined with a projected rotational velocity of 7 km/s. The star is radiating 292 times the Sun's luminosity from its photosphere at an effective temperature of 13,200 K.

2 Persei

2 Persei is a binary star system in the northern constellation Perseus, located around 500 light years away from the Sun. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude is 5.70. The system is moving further away from the Earth with a heliocentric radial velocity of 11 km/s.In 1970 radial velocity measurements from spectrograms taken at David Dunlap Observatory indicated it was a single-lined spectroscopic binary. Follow up observations led to the determination that it had a nearly circular orbit with a period of 5.6 days. The visible component is a chemically peculiar mercury-manganese star with a stellar classification of B9pHgMn. Other analyses of its spectrum have assigned it the giant star spectral type of B9III.

36 Lyncis

36 Lyncis is a solitary variable star located around 570 light years away from the Sun in the northern constellation of Lynx. It has the variable star designation of EI Lyncis, while 36 Lyncis is the Flamsteed designation. This object is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of 5.30. It is moving further away from the Earth with a heliocentric radial velocity of 21 km/s.This is a magnetic, helium-weak Bp star with a stellar classification of B8 IIImnp. It is sometimes classified as a mercury-manganese star. It is also an 'sn' star, displaying a spectrum with generally sharp lines for most elements in combination with broad, diffuse lines of helium. 36 Lyncis has been classified as an SX Arietis variable with an amplitude of 0.03 in visual magnitude and a rotationally-modulated period of 3.834 days. The star is spinning with a projected rotational velocity of 49 km/s and a rotation rate of 3.83476 days. It has 4.21 times the Sun's radius and is radiating 443 times the luminosity of the Sun from its photosphere at an effective temperature of 13,700 K.

56 Aquarii

56 Aquarii, abbreviated 56 Aqr, is a star in the constellation of Aquarius. 56 Aquarii is its Flamsteed designation. It is a sixth magnitude star, having an apparent visual magnitude of 6.36, and thus is a challenge to view with the naked eye. Based upon an annual parallax shift of 5.07 mas, it is located around 643 light years from the Earth. At that distance, the visual magnitude is diminished by an extinction of 0.12 due to interstellar dust. The star is moving closer with a heliocentric radial velocity of −28 km/s. It is a candidate runaway star showing a transverse peculiar velocity of 213.87 km/s.Houk and Smith-Moore (1978) gave this star a stellar classification of B8 II, matching a B-type bright giant. In contrast, Cowley et al. (1969) found a class of B8 Vs, corresponding to a B-type main-sequence star with narrow ("sharp") absorption lines due to a relatively low projected rotation. Zorec and Royer (2012) modeled it as a dwarf star that is 67% of the way through its main sequence lifespan. It is a chemically peculiar mercury-manganese star, showing abnormally strong absorption lines of mercury and magnesium with weak lines of helium. The star has 3.4 times the mass of the Sun and about 2.8 times the Sun's radius. It is radiating 185 times the Sun's luminosity from its photosphere at an effective temperature of 11,912 K.

66 Eridani

66 Eridani is a binary star in the constellation of Eridanus. The combined apparent magnitude of the system is 5.12 on average. Parallax measurements by Hipparcos put the system at some 309 light-years (95 parsecs) away.This is a spectroscopic binary: the two stars cannot be individually resolved, but periodic Doppler shifts in its spectrum mean there must be orbital motion. The two stars orbit each other every 5.5226013 days. Their orbit is fairly eccentric, at 0.0844.The combined spectrum of 66 Eridani matches that of a B-type main-sequence star, and the two stars have similar masses. The spectrum also shows excess of mercury and manganese, as it is a type of chemically peculiar star called a mercury-manganese star. 66 Eridani is a Alpha2 Canum Venaticorum variable. For this reason, it has been given the designation EN Eridani.

AR Aurigae

AR Aurigae (AR Aur), also known by its Flamsteed designation 17 Aurigae, is a binary star in the constellation Auriga. Based on parallax measurements made by the Hipparcos spacecraft, it is approximately 400 light-years from Earth.Both components are blue-white B-type main-sequence stars that do not fill their Roche lobes. The system has a mean apparent magnitude of +6.15. However, the orbit of the stars are oriented in such a way that they periodically eclipse each other, so AR Aurigae is a variable star and its brightness varies from magnitude +6.15 to +6.82 with a period of 4.13 days.The primary component of AR Aurigae is known to be a mercury-manganese star, also known as an HgMn star. As the name implies, these stars have over-abundances of the elements mercury and manganese, and also often xenon and other elements. Because AR Aurigae is an eclipsing binary (in fact, it is the only known eclipsing binary with a mercury-manganese star), accurate characterization of its parameters has been made possible. Based on the light-time effect observed from the stars, it is inferred that there is a third star with a mass of 0.54 M☉, orbiting at a separation of 13 au every 23.7 years.

Alpha Andromedae

Alpha Andromedae (α Andromedae, abbreviated Alpha And or α And), officially named Alpheratz , is located 97 light-years from the Sun and is the brightest star in the constellation of Andromeda. Located immediately northeast of the constellation of Pegasus, it is the upper left star of the Great Square of Pegasus.

Although it appears to the naked eye as a single star, with overall apparent visual magnitude +2.06, it is actually a binary system composed of two stars in close orbit. The chemical composition of the brighter of the two stars is unusual as it is a mercury-manganese star whose atmosphere contains abnormally high levels of mercury, manganese, and other elements, including gallium and xenon. It is the brightest mercury-manganese star known.

Beta Sculptoris

Beta Sculptoris, Latinized from β Sculptoris, is a single, blue-white hued star in the southern constellation of Sculptor. It has an apparent visual magnitude of 4.37, which is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 18.74 mas as seen from Earth, it is located 174 light years from the Sun.

This is a B-type giant star with a stellar classification of B9.5IIIp(HgMnSi). It belongs to the class of chemically peculiar stars known as a Mercury-Manganese star, showing overabundances of mercury, manganese, and silicon in its spectrum. It is a suspected α2 CVn variable with magnitude variation from 4.35 to 4.39. The star has nearly three times the mass of the Sun and double the Sun's radius. It is radiating 81 times the Sun's luminosity from its photosphere at an effective temperature of 12,110 K.

Chi Lupi

Chi Lupi (Chi Lup, χ Lupi, χ Lup) is a spectroscopic binary star in the constellation of Lupus. It has an apparent visual magnitude of approximately 3.957. The primary star in the binary is a mercury-manganese star of spectral type B9.5V; the secondary is a metallic-lined star of type A2Vm.This system is a proper motion member of the Upper Scorpius sub-group in the

Scorpius-Centaurus OB association,

the nearest such co-moving association of massive stars to the Sun.

The Upper Scorpius subgroup contains thousands of stars with an average age of 11 million years old at mean distances of 145 parsecs (470 light years).

HD 30963

HD 30963 is a star in the constellation of Eridanus. With an apparent magnitude of 7.23, it cannot be seen with the naked eye. Parallax measurements made by Hipparcos put the star at a distance of around 900 light-years (280 parsecs) away.HD 30963 is a late B-type star. It is a mercury-manganese star, a class of chemically peculiar star that has an overabundance of certain elements like mercury. HD 30963 has 150,000 times as much mercury, 2,500 times as much platinum, 1,000 times as much yttrium, and 150 times as much zirconium compared to the Sun. It has a mass of 2.90 M☉, and its surface temperature is about 11,500 K.HD 30963 is close to the orbit that the solar system is traversing in the Milky Way. The sun will be close to the current location of HD 30963 in about 18.5 million years. Interstellar absorption lines for Na I are present for velocities lower than 10 km/s.

HD 3322

HD 3322 is a binary star system in the northern constellation of Andromeda. With an apparent visual magnitude of 6.51, it lies below the nominal brightness limit for visibility with the normal naked eye, but it is still possible to see the star with excellent vision under ideal seeing conditions. An annual parallax shift of 4.59±0.65 mas provides a distance estimate of roughly 700 light years.

This is a single-lined spectroscopic binary star system with an orbital period of around 400 days and an eccentricity of 0.57. The visible component has a stellar classification of B8.5 IIIp HgMn, matching a chemically peculiar B-type giant mercury-manganese star. Catalano and Leone (1991) found it to be a α2 CVn variable with a period of 4.6904 days, and thus it received the variable star designation PY And. It has an estimated 3.7 times the mass of the Sun and about 4.8 times the Sun's radius. It is radiating around 246 times the Sun's luminosity from its photosphere at an effective temperature of 12,882 K.

Iota Coronae Borealis

Iota Coronae Borealis, Latinized from ι Coronae Borealis, is a binary star system in the constellation Corona Borealis. It is visible to the naked eye with a combined apparent visual magnitude of is 4.96. Based upon an annual parallax shift of 10.46 mas as seen from the Earth, it is located about 312 light years from the Sun.

This is a single-lined spectroscopic binary with an orbital period of 35.5 days and an eccentricity of 0.56. The visible member, component A, has a stellar classification of A0 IIIp(HgMnEu)s, indicating it is a chemically peculiar mercury-manganese star with narrow absorption lines. The secondary member, component B, appears to be an A-type star.

Kappa Cancri

Kappa Cancri, Latinized from κ Cancri, is a blue-white hued binary star system in the zodiac constellation of Cancer. It is faintly visible to the naked eye with an apparent visual magnitude of +5.23. The magnitude difference between the two stars is about 2.6. Based upon an annual parallax shift of 7.13 mas as seen from the Earth, the system is located roughly 460 light years from the Sun.

This is a single-lined spectroscopic binary star system with an orbital period of 6.39 days and an eccentricity of 0.13. The primary, component A, has a stellar classification of B8 IIIp, suggesting it is a B-type giant star. It a mercury-manganese star, a type of chemically peculiar star showing large overabundances of those two elements in the outer atmosphere. It is classified as an Alpha2 Canum Venaticorum type variable star and its brightness varies from magnitude +5.22 to +5.27 with a period of 5 days.The primary component has 4.5 times the mass of the Sun, 5 times the Sun's radius, and an effective temperature of 13,200 K. The secondary, component B, is a smaller star with 2.1 times the mass and 2.4 times the radius of the Sun, having an effective temperature of 8,500 K.

Maia (star)

Maia , designated 20 Tauri (abbreviated 20 Tau), is a star in the constellation of Taurus. It is the fourth-brightest star in the Pleiades open star cluster (M45), after Alcyone, Atlas and Electra, in that order. Maia is a blue giant of spectral type B8 III, and a mercury-manganese star.

Maia's visual magnitude is 3.871, requiring darker skies to be seen. Its total bolometric luminosity is 660 times solar, mostly in the ultraviolet, thus suggesting a radius that is 5.5 times that of the Sun and a mass that is slightly more than 4 times solar. It was thought to be a variable star by astronomer Otto Struve. A class of stars known as Maia variables was proposed, which included Gamma Ursae Minoris, but Maia and some others in the class have since been found to be stable.Maia is surrounded by the Maia Nebula (also known as NGC 1432), one of the brightest patches of nebulosity within the Pleiades star cluster.

Phi Herculis

Phi Herculis (φ Her) is a binary star system in the northern constellation of Hercules. Based upon an annual parallax shift of 15.99 mas as seen from Earth, it is located around 204 light years from the Sun. With a combined apparent visual magnitude of 4.24, it is bright enough to be seen with the naked eye.

This is a single-lined spectroscopic binary star system with an orbital period of 564.8 days and an eccentricity of 0.526. The primary, component A, is a B-type main sequence star with a stellar classification of B9VspHgMn. It is a chemically peculiar star of the type called a mercury-manganese star. The star is tentatively cataloged as a Alpha2 Canum Venaticorum variable.The secondary, component B, was first separated via interferometry in 2004. It is an A-type main sequence star of class A8V. The magnitude difference between the two components is 2.64.

Rho Aquarii

Rho Aquarii, Latinized from ρ Aquarii, is the Bayer designation for a binary star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of +5.34. Based upon parallax measurements made during the Hipparcos mission, this star is at a distance of roughly 880 light-years (270 parsecs) from Earth.This is a single-lined spectroscopic binary, with the presence of a companion being revealed by Doppler shifts in the spectrum. The primary is a giant star with a stellar classification of B8 IIIp Mn:Hg:. It is a Mercury-Manganese star, showing a surfeit of these elements in the spectrum. With five times the Sun's mass, this star is radiating 1,035 times as much luminosity from its outer atmosphere at an effective temperature of 12,593 K. This heat gives it the blue-white hue of a B-type star. The companion may be a variable star.

Zeta Canis Minoris

Zeta Canis Minoris (ζ Canis Minoris) is a solitary, blue-white hued star in the equatorial constellation of Canis Minor. It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.13. Based upon an annual parallax shift of 5.23 mas as seen from Earth, this star is located around 410 light years from the Sun. It is moving away from the Sun with a radial velocity of +32.3 km/s.This is a B-type bright giant star with a stellar classification of B8 II. It is a Mercury-Manganese star, showing an overabundance of these elements in its spectrum. The mean longitudinal magnetic field strength is 8.28±11.55 G. The star has about four times the mass of the Sun and is radiating 490 times the Sun's luminosity from its photosphere at an effective temperature of 13,500 K.

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